The present disclosure relates to a stirring conveyance member, a developing device, and an image forming apparatus. The stirring conveyance member conveys a powder such as a developer while stirring the powder. The developing device includes the stirring conveyance member. The developing device is installed in the image forming apparatus.
In an image forming apparatus, a latent image is formed on a surface of an image bearing member constituted by a photosensitive member or the like, and the latent image is visualized as a toner image through development by a developing device. Developing methods include a two-component developing method using a two-component developer. A developing device employing the two-component developing method includes a developer container, a development roller, and a stirring conveyance member. The developer container accommodates a developer including a carrier and a toner. The development roller supplies the developer to the image bearing member. The stirring conveyance member conveys and supplies the developer from the developer container to the development roller while stirring the developer.
In the two-component developing method, image defects such as scattering of the toner and fogging may occur when the toner is insufficiently charged. Therefore, it is necessary to charge the toner to a specific level by sufficiently mixing the toner and the carrier through stirring.
Under the above circumstances, a powder stirring conveyance member includes a shaft member and a sub-conveyance part. Along with rotation of the shaft member, a main conveyance blade conveys a powder in a first direction that is an axial direction. Along with rotation of the main conveyance blade and the shaft member, the sub-conveyance part generates a conveying effect by which some of the powder is conveyed in a second direction that is another axial direction. The sub-conveyance part is a sub-conveyance blade, for example. The sub-conveyance blade has a smaller diameter than the main conveyance blade, and is wound in a direction opposite (in a phase opposite) to the main conveyance blade.
Further, another stirring conveyance member includes a rotary shaft, a first spiral blade, and a second spiral blade. The first spiral blade is formed on the outer circumferential surface of the rotary shaft. The first spiral blade conveys a powder in an axial direction through rotation of the rotary shaft. The second spiral blade is formed on the outer circumferential surface of the rotary shaft such that a region in which the first spiral blade is formed overlaps with a region in which the second spiral blade is formed. The second spiral blade is in a phase opposite to the first spiral blade. The second spiral blade has a lower height in a radial direction than the first spiral blade. The first spiral blade and the second spiral blade each have a trapezoidal cross section in a plane transverse to the lengthwise direction of the spiral blade. In each turn of the first spiral blade around the rotary shaft, the first spiral blade has a plurality of first expanded parts each having a larger base of the trapezoidal cross section than the other parts. In each turn of the second spiral blade around the rotary shaft, the second spiral blade has a plurality of second expanded parts each having a larger base of the trapezoidal cross section than the other parts. In each turn around the rotary shaft, the base of the trapezoidal cross section is expanded in each of the plurality of first expanded parts and the plurality of second expanded parts than in the other parts. In the stirring conveyance member, the first spiral blade and the second spiral blade intersect each other in at least one of the first expanded parts in each turn around the rotary shaft.
According to the above configuration, the second spiral blade (the sub-conveyance blade) generates conveying force in a direction opposite to a conveyance direction of the developer by the first spiral blade (the main conveyance blade), and as a result, a convective flow is generated in a portion of the developer being conveyed. Therefore, a stirring effect is promoted with almost no inhibition of a conveying effect of the first spiral blade (the main conveyance blade).